Biomedical subjects

N Kerscher

Publications and source records attributed to N Kerscher.

3 recordsLinked to original sources

PubMed2001

Changes of contrast gain in cat dorsal lateral geniculate nucleus by dopamine receptor agonists.

The modulatory effects of dopamine (DA) on the contrast gain of retino-geniculate transmission were tested with local micro-iontophoretical application of DA and the DA receptor agonists SKF38393 (SKF, D1/D5) and quinpirole (QUIN, D2/D3/D4) while recording visually induced spike activity of relay cells of the dorsal aspect of cat lateral geniculate nucleus (dLGN) in the anesthetised and paralyzed preparation. DA and QUIN could either facilitate or inhibit visual activity in a dose-dependent fashion: small amounts caused a facilitation while larger quantities resulted in a more (DA) or less (QUIN) strong inhibition. The effect of SKF was almost always suppressive and increased with the amount of drug applied. The absolute change in activity was depending on stimulus contrast and the strength of the elicited response: facilitation and inhibition of activity was proportional to stimulus contrast and response strength and thus resulted in a changed contrast gain. The results indicate that the visual deficits found in Parkinson's disease patients my be not solely related to retinal dysfunctions.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗

PubMed1998

State-dependent receptive-field restructuring in the visual cortex.

To extract important information from the environment on a useful timescale, the visual system must be able to adapt rapidly to constantly changing scenes. This requires dynamic control of visual resolution, possibly at the level of the responses of single neurons. Individual cells in the visual cortex respond to light stimuli on particular locations (receptive fields) on the retina, and the structure of these receptive fields can change in different contexts. Here we show experimentally that the shape of receptive fields in the primary visual cortex of anaesthetized cats undergoes significant modifications, which are correlated with the general state of the brain as assessed by electroencephalography: receptive fields are wider during synchronized states and smaller during non-synchronized states. We also show that cortical receptive fields shrink over time when stimulated with flashing light spots. Finally, by using a network model we account for the changing size of the cortical receptive fields by dynamically rescaling the levels of excitation and inhibition in the visual thalamus and cortex. The observed dynamic changes in the sizes of the cortical receptive field could be a reflection of a process that adapts the spatial resolution within the primary visual pathway to different states of excitability.

Animals↗

PubMedDate not supplied

High-frequency (300-800 Hz) components in cat geniculate (dLGN) early visual responses.

We analysed the early visual responses of relay cells of the dorsal part of cat lateral geniculate nucleus (dLGN) for the occurrence and characteristics of high-frequency (>300 Hz) spike patterns comparable to the high-frequency oscillations (HFO) found in the human somatosensory system. By using a special algorithm for correcting response latency, we can show that the vast majority of dLGN visual responses which were elicited by a sudden change in contrast show HFOs in the range of 300 to more than 800 Hz. After response time correction these HFOs are clearly visible in summed responses, indicating that these patterns are highly reproducible by identical stimuli. On this basis we analysed the HFOs in more detail. We found the oscillation frequency to increase with stimulus contrast and the area of the receptive field centre covered by an excitatory stimulus. Inhibition reduces the oscillation frequency as demonstrated with additional stimulation of the antagonistic surround of the receptive field and by blocking inhibition with micro-iontophoretical application of bicuculline methiodide. The HFO was almost independent of the state of the system as estimated from the EEG pattern. Based on these findings we discuss whether bursts of action potentials triggered by the low-threshold calcium spike (LTS) can contribute to this pattern of visual thalamic activity.

Action Potentials↗